Background and Aims
Declining autumn and winter rainfall increasingly limits soil moisture availability at the onset of the growing season in southern Australia. We studied the consequences of reduced rainfall during dormancy on vine growth, and explored irrigation strategies to maintain yield following dry winters.
Methods and Results
The effect of the timing and method of irrigation during dormancy on vine performance was investigated for three seasons in a Shiraz vineyard where late autumn and winter rainfall was excluded using shelters. Reduced soil moisture in spring delayed the time of budburst. A reduction in rain to approximately one third of the historical average reduced yield (24–42%) and canopy size (16–31%). Natural rain (Control) or equivalent sprinkler irrigation, providing water during winter, resulted in a higher yield: pruning mass ratio, but reduction in yield was still observed when drip irrigation was used to replace winter rain. Refilling the soil profile in spring after dry winters favoured growth partitioning towards canopy and roots, increased carbohydrate reserves in the trunk, but reduced yield (−10 to −32%).
Conclusions
Irrigation during winter did not fully offset the decline in production. Refilling the soil profile at the end of winter increased vigour, and reduced yield. Reduced soil moisture prior to spring delayed the time of budburst.
Significance of the Study
Vineyard management aiming to sustain yield under a changing climate will need to incorporate winter irrigation. Models predicting the time of budburst under a changing environment could be fine‐tuned by incorporating soil moisture availability.
Potted Cardinal, Chardonnay, and Chenin blanc vines were subjected to heat stress of 40°C and 20°C (day and night temperatures, respectively) for periods of 0 (control), four, eight, and 12 days before returning the vines to optimal day temperature conditions of 25°C to 29°C in a greenhouse for an eight-day "recovery period". Root temperatures were maintained constant during the heat stress period by holding the pots in a water bath. Stomatal conductance, predawn leaf water potential, air and leaf temperatures, relative humidity, and photosynthetic active radiation were measured throughout the experiment. Heat stress markedly reduced stomatal conductance (Cs)in Chardonnay and Chenin blanc vines. Under optimal temperature conditions (25 ° to 29°C/15 ° to 16°C day/night temperatures), Chardonnay vines had the highest Cs, followed by Chenin blanc and Cardinal, whereas under heat stress (40°C), Chenin blanc had the highest Cs, followed by Chardonnay and Cardinal. However, Cardinal was the least affected of the three cultivars. Within one to four days after heat-stressed vines were returned to optimal day temperature conditions, Cs was similar to that of control vines.
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